SIEGEL: The BBC has announced that the latest actor to play its time-traveling alien is a woman, Jodie Whittaker. She'll take over from the current Doctor, Peter Capaldi, at Christmas. Our resident "Doctor Who" fanatic Petra Mayer is here now to talk about the transition. And, Petra, for those who aren't so familiar with "Doctor Who," first, why have there been so many Doctors?

PETRA MAYER, BYLINE: Ah, that's the important question here. The show began way back in 1963 with William Hartnell, and it was a huge hit. And as they went along, Hartnell was getting older. He was - eventually he was too ill to perform the role, and they had to come up with some way to keep the show going without him. So their solution was kind of ingenious. He's an alien. This is a fictional show. We can do what we want. He will just magically become someone else when he gets old and sick enough or injured enough. And so that's where the concept of regeneration comes from. William Hartnell became Patrick Troughton, the second Doctor, and onward from there.

SIEGEL: And now to Jodie Whittaker. Where have we seen her before?

MAYER: Americans who have seen her before will probably have seen her in the British detective series "Broadchurch." She played the mother of the boy whose murder was at the center of the first season. And there's kind of this whole web of connections there. You know, David Tennant was one of the stars of "Broadchurch." He was the tenth Doctor. Olivia Colman, the other star, had also had a bit role. Chris Chibnall, who is now taking over as the showrunner, was one of the main writers of "Broadchurch." So, you know, it's an infinite universe, but it's a really small world.

SIEGEL: What are "Doctor Who" fans saying about Jodie Whittaker and the idea of a woman playing the part?

MAYER: Oh, well, I've been having a lot of laughs watching the #dr13 hashtag on Twitter, I'll tell you that much. Whittaker did do an interview with the BBC after the announcement where she said to fans, please don't be afraid of my gender. The nature of this character is change, right? And I think overall the reaction's been pretty positive. You know, there are always going to be people yelling about political correctness and they'll never watch the show again, which is kind of part of the tradition of "Doctor Who," is people flouncing because some change in the casting or writing upsets them.

The one important criticism that I kind of do want to point out - I've seen a lot of fans talking online about that we should just take a moment to pause the celebrations and to remember that The Doctor's a woman, but she is still a white woman. And the show has made it canonical, in fact, that Time Lords can change gender as well as race. So I think a lot of fans out there are wondering - and they're disappointed that there's not yet an actor of color playing the part.

SIEGEL: We are talking about an ancient time-traveling alien - a Time Lord, yes?

MAYER: A Time Lord, yes.

SIEGEL: Two hearts, and he or she can do whatever he or she wants.

MAYER: Sure, yeah. I mean, the canon of the show - right? - traditionally is that there is no canon. You have all of time and space to play with. You can do whatever you want. But it has been running for 50 years, and there's, you know, a huge and dedicated fan base that has a very deep connection to the show as they know it. And it is true that apart from, you know, a comedy short in the '90s The Doctor has never been a woman. So it's really cool that Steven Moffat, who's the outgoing showrunner, he's been really building up a foundation. A couple seasons ago we actually saw The Master, who's The Doctor's big frenemy, regenerate as a woman called Missy. And then, of course, in the season finale just a couple weeks ago there was this delightful little Easter egg.

(SOUNDBITE OF TV SHOW, "DOCTOR WHO")

JOHN SIMM: (As The Master) Is the future going to be all girl?

PETER CAPALDI: (As The Doctor) We can only hope.

SIEGEL: (Laughter) I encountered "Doctor Who" living in London in the - I guess the Tom Baker era. He was...

MAYER: The fourth Doctor.

SIEGEL: ...The fourth Doctor.

MAYER: Sure. Would you care for a jelly baby?

SIEGEL: He traveled around - The Doctor was transported, I guess, from one dimension to the next by a TARDIS, his TARDIS.

MAYER: Yeah.

SIEGEL: A flying - the Brits would say call box, we'd say a phone booth. There aren't that many phone booths in the world anymore.

MAYER: No. Well, the TARDIS, if you want to be real specific about it, is a police call box. And it stands for Time and Relative Dimensions in Space. So it is his - yeah, it's his spacecraft. He can go wherever and whenever he wants in it.

SIEGEL: And it will be hers as well?

MAYER: It will be hers. In the short where they - the BBC made a little announcement video, and the final scene was Jodie Whittaker walking up to the TARDIS as it appears in a forest. And my singular human heart went pitter-pat (ph). It was very exciting.